Nanotubes make fluid filter

Researchers from Rensselaer Polytechnic
Institute have devised a simple and inexpensive way to manufacture very
fine filters from carbon nanotubes.

Carbon nanotubes are rolled-up sheets of carbon atoms that can
be narrower than 1 nanometer, which is about the span of 10 hydrogen atoms.

The researchers showed that the filters could be used to separate
heavy hydrocarbons from petroleum and bacteria and viruses from water.

Filtering heavy hydrocarbons is a crucial step in distilling crude
oil. The filters are capable of filtering viruses as small as 25 nanometers,
including the especially tiny polio virus, according to the researchers.

The researchers fabricated well-organized filtration tubes as
long as five centimeters that consist solely of nanotubes. They made the
filter by using argon gas to force a benzene-ferrocene solution through
a spray nozzle into a quartz tube, then heating the solution to 900 degrees
Celsius. The formation of large carbon nanotube structures is dependent
on the size of the spray nozzle and the flow rate of the solution, according
to the researchers.

The process is inexpensive, relatively easy, and allows for specific-size
pores, making for specific types of filters, according to the researchers.
Because carbon nanotubes are very strong and heat-resistant, the filters
can be cleaned using heat and ultrasound and reused.

The researchers' method could be used to make practical filters
within five years, according to the researchers. The work appeared in
the August 1, 2004 issue of Nature Materials.